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An Overview of Different Topologies of DC/DC Bidirectional Converter for
Different Applications
Chapter · February 2020
DOI: 10.1007/978-981-15-1616-0_70
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3. 722 S. Sathishkumar et al.
2 Overview of Different Topologies
In [1], bidirectional converter has been presented that consists of LLC-C resonant
converter with symmetry resonant tank as shown in Fig. 1a. It is used for the energy
storage system. In this topology, MOSFETs S-P and S-S auxiliary switches are pro-
vided to bypass the resonant capacitors. This topology is shown in Fig. 1. It is used
to interface the dc voltage bus and the battery. The dc voltage bus is connected to the
primary of the transformer and the battery is connected to the secondary side. It con-
sists of MOSFETs S1–S4 acting as chopping full bridge converter, MOSFETs S5–S8
acting as rectification full bridge converter, resonant tank and auxiliary switches.
The resonant tank is connected between chopper and rectification full bridge which
includes transformer T, resonant capacitors Cr1 and Cr2, resonant inductor Lr.
V1 is the dc voltage bus and V2 is the battery. By taking battery charging mode
as forward mode, S-P turned OFF and S-S turned ON which bypasses the resonant
capacitor Cr2. Therefore, the resonant tank in this mode was standard LLC network.
In this mode, resonant converter parameters are given in (1), (2), (3) and (4).
Series resonant frequency fr1 = 1/2π
LrCr (1)
Fig. 1 Presented topologies in; a [1]; b [2]; c [3]; d [4]; e [5]; f [6]; g [7]; h [8]; i [9]
4. An Overview of Different Topologies of DC/DC Bidirectional … 723
Inductance ratio m = (Lm + Lr)/Lr (2)
Positive characteristics impedance Z1 =
Lr/Cr1 (3)
Transformer ratio n =
n1
n2
(4)
In the reverse mode, S-P turned ON and S-S turned OFF which bypasses the
resonant capacitor Cr1. Then Cr2, Lm and Lr form the CLL resonant tank network.
The CLL network can be transformed into the LLC network by using the following
expressions (5):
⎧
⎪
⎨
⎪
⎩
Lr = Lr Lm
Lr+Lmn2
Lm = Lm/(Lr + Lm)n2
n
= n(Lr+Lm)
Lm
(5)
The proposed topology has the same gain for both charging and discharging mode.
In [2], a new topology for bidirectional resonant DC-DC converter is presented
as shown in Fig. 1b. It is suitable for applications requiring high voltage gain for
wider range. It has very high gain and efficiency throughout the operating range
of the voltage. Fixed-frequency phase-shift modulation is used instead of variable-
frequency modulation to maintain the normalized gain irrespective of the loads.
The proposed topology has primary and secondary circuits connected to a trans-
former T as shown in Fig. 1b. The secondary circuit operates in two switching modes:
full-bridge (FB) mode and half-bridge (HB) mode. In FB mode and HB mode, the
circuit operates as LLC resonant converter and series resonant converter then the
voltage across the transformer winding is ±Vs and ±Vs/2, respectively.
Ineachswitchingcycle,bothFBandHBmodeoccurs.Thepowertransferbetween
primary and secondary sides is adjusted by controlling the time interval ratio of the
two modes. In reverse power flow, Lm is clipped by voltage ucd and circuit acts as LC
series resonant converter. In forward power flow, Lm is connected and circuit acts as
LLC resonant converter. The LC series resonant frequency f r is given by (6).
fr =
1
2π
√
Lr(Cr1 + Cr2)
(6)
Throughout the cycle, the secondary current is is given by subtracting current
through the magnetizing inductor (iLm
) from the current through resonant inductor
(iLr
). High efficiency can be achieved, i.e. 98.3 and 98.2% from small load to full
load in forward and reverse power flow.
In [3], DeshangSha proposed an innovative topology of bidirectional three-level
DC-DC converter which achieved full zero voltage switching (ZVS) as shown in
Fig. 1c and used for battery charging and discharging in electric vehicle technology.
The circuit is designed with Reduced Circulating Loss using double pulse-width
5. 724 S. Sathishkumar et al.
modulation (PWM) and double-phase-shifted control. The ZVS of all the switches
can be achieved by utilizing the magnetizing current and transformer magnetizing
inductance should be designed accurately.
The magnetic bias issue of the clamp capacitor is eliminated by connecting same
capacitor Cc1 across the parallel-connected two-buck converter. The output power
of the converter during charging mode with T∅1 T∅2 is given:
When D ∈ [0.5, 0.75), P0 is given by (7) as,
⎧
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎨
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎩
V 2
Cc2
T Lr
2(1 − D)T T∅1 − T 2
∅1
, T∅1 ∈ [0, T∅2)
V 2
Cc2
T Lr
2(1 − D)T T∅1 − (T∅1 − T∅2)2
− T 2
∅1
,
T∅1 ∈ [T∅2, (1 − D)T )
V 2
Cc2
T Lr
(1 − D)2
T 2
− (T∅1 − T∅2)2
,
T∅1 ∈ [(1 − D)T, 0.5T ]
(7)
When D ∈ [0.75, 1], P0 is given by (8) as,
⎧
⎪
⎪
⎪
⎪
⎨
⎪
⎪
⎪
⎪
⎩
V 2
Cc2
T Lr
2(1 − D)T T∅1 − T 2
∅1
, T∅1 ∈ [0, (1 − D)T ]
V 2
Cc2
T Lr
(1 − D)2
T 2
, T∅1 ∈ [(1 − D)T, T∅2)
V 2
Cc2
T Lr
(0.5T − T∅1)[(1.5 − 2D)T + T∅1],
T∅1 ∈ [T∅2, 0.5T ]
(8)
The output power during discharging mode is determined in the same way. The
voltage conversion gain is given by (9) as,
G =
2n
1 − D
(9)
The circuit operates under ZVS condition throughout the loading conditions. The
efficiency of this converter is 96.71% in charging mode and 96.79% in discharging
mode.
In [4], three-level bidirectional DC-DC converter topology is proposed with Zero
Voltage Transition in both bucks and boost operations. Two ZVT cells are connected
toemploysoftswitchingandtoturnonalltheswitchesbelowzerovoltageasshownin
Fig. 1d. ZVT cell consists of two inductors, a capacitor and a supplementary switch.
As soft-switching operation is dependent on output current, its operating range is
restricted. The resonant inductors should have same values to avoid unbalancing. To
achieve ZVT, the time between turning off of Sa2 and turning on of switch S2 should
be kept small.
6. An Overview of Different Topologies of DC/DC Bidirectional … 725
The minimum value of Lr operating at constant load is
Lr ≥
V0
4iLr2 (t0)
t45 (10)
In (10), current is constant at t46.
Under variable load, minimum value of Lr should be
Lr ≥
V0
4iLr2 (t0)
tZVT (11)
In (11), the zero voltage transition takes place at tZVT.
Voltage across the switches (Vmain) is the addition of half the output voltage and
the voltage across the resonant capacitor is given as
Vmain =
V0
2
+ iLr2 (t0)
2Lr
Cr1
(12)
The unbalanced dc-link capacitor voltages caused by unsymmetrical network and
delays caused by gate driver circuit should be eliminated by adjusting the duty cycle
of the main switches by allowing capacitors to charge and discharge according to
dc-link capacitance.
In [5], multiport converter is proposed used to connect different dc sources to a
grid. It consists of less number of switches and manages the concurrent power sources
of solar PV system as shown in Fig. 1e. The soft switching of the main switches
is achieved by inductor-capacitor-inductor (LCL) resonant circuit. The battery and
solar PV system are connected to the bidirectional and unidirectional port, respec-
tively. The charge controller is used to govern the battery charging and discharging
operations to avoid over-charging and over-discharging.
The transformer is used to connect the high voltage side (HVS) with the low
voltage side (LVS). The primary of transformer is connected to the battery, solar
PV system and the LCL resonant circuit. The secondary side is connected to a full
bridge rectifier. Switch 1 is called main switch as it not only controls the source but
also controls the direction of current through the transformer. When excess power is
produced by the solar than the load required, then S3 is opened and S2 is closed to turn
on the buck converter. Then excess power is stored in the battery. When generated
solar power is smaller than the power required, then it acts as a boost converter
supplying power from the battery. The transfer function between the battery current
(ibat(s)) and duty cycle (d2(s)) of the switch S2 in the forward mode is obtained as
shown in (13).
Gc(s) =
ibat(s)
d2(s)
=
(V1 − Vbat) · s + 1
rb·C2
s2 + r2
L2
+ 1
rb·C2
s +
r2
rb
+D2
L2·C2
(13)
7. 726 S. Sathishkumar et al.
The transfer function between the battery current and duty cycle of the switch S3
in the reverse mode is given by (14)
Gd(s) =
ibat(s)
d3(s)
=
V1 · s + 1
rb·C2
s2 + r2
L2
+ 1
rb·C2
s +
r2
rb
+1
L2·C2
(14)
Then PI controller is used to produce duty cycle for S2 and S3 by using current
error as input. This multiport converter has efficiency of 94.5%.
In [6], a bidirectional converter for automotive application with digital control is
proposed as shown in Fig. 1f. The pulses having preferred frequency applied to the 9
MOSFETs are generated by FPGA. It consists of 2 current bridge converter (H and
L) separated by high-frequency transformer TR. When the power is transmitted from
L to H converter, L acts as an inverter and H acts as a rectifier and H to L, L acts as
a rectifier and H acts as an inverter. The amount of energy transfer is controlled by
switching frequency. Series-parallel resonant circuit consisting of capacitors CL, CH
and inductance LH is used for switching of both inverters. When switching frequency
is decreased, the amount of energy transfer is increased and vice versa. The output
of digital multi-channel pulse frequency modulator (DPFM) from FPGA is given
to the converter switches. The desired frequency and time constants are entered in
DPFM module by the user. Capacitor C is connected to perform soft switching in
the H converter.
In [7], Rathore and the team proposed non-isolated bidirectional resonant dc/dc
converter for micro gird applications. The circuit consists of front-end current fed
half-bridge boost converter, resonant LCL tank and voltage doubler at high voltage
side to increase the gain as shown in Fig. 1g. For entire boost operation, switches
M3 and M4 are in off condition. M1 and M2 are in off condition for buck operation.
The buck operation is attained by dividing high voltage side using capacitor divider
circuit and produces higher step-down ratio. Then VH/2 is applied to the resonant
circuit from high voltage side.
The voltage gain of the converter at boost mode is given by (15) as
VH =
VL · Gboost · 2
1 − D
(15)
where D = duty cycle, VL/1 − D = boost converter gain, Gboost =
(XLr2
+Rac)Rac
(XLr1
+XCP )(XLr2
+Rac)
and 2 is voltage doubler gain. The voltage gain of the converter
at buck mode is given by (16) as
VL = 0.5VH · DbuckGbuck (16)
where Gbuck =
Xcp Racb
XLr1
Xcp +XC6
XCP
+XLr1
XLr2
+XC1
XLr1
+XCP
XLr1
. Zero Voltage Switching
(ZVS) is carried out to turn on all the switches whereas Zero Current Switching
(ZCS) is achieved on all the diodes on both turn on and turn off.
8. An Overview of Different Topologies of DC/DC Bidirectional … 727
In [8], bidirectional DC/DC converter with resonant tank is proposed for charging
and discharging applications as shown in Fig. 1h. The resonant tank used is CLLLC
type. The paper ensures the soft switching of all switches without help of snubber
or clamp circuit. So high-frequency switching is enabled and size of components
is reduced. In forward mode, power is transferred from dc bus to battery and in
regeneration mode the power is transferred from battery to dc bus. The circuit has
symmetrical converters. One acts as inverter and other acts as converter. They are
separated by resonant network.
The fundamental voltage vAB and vC D is given by Eqs. (17) and (18),
vAB =
4VDC
π
· sin(ωst) (17)
vC D = sign(i2) · V0 (18)
The CLLC resonant network is derived from CLLLC network to reduce the num-
ber of magnetics. The magnetics comparison of CLLLC and CLLC resonant con-
verter is tabulated. To eliminate start-up surge current, capacitor and inductor are
connected at the secondary side and switching frequency is kept higher than the
normal frequency at the starting.
In [9], multiple-input bidirectional isolated DC/DC converter is proposed for
energy storage system using battery as shown in Fig. 1i. Any dc sources can be given
as input to the ports. Dual active bridge converter is used, it acts in combination
and independent mode. In independent mode, this converter operates at wide range
with high efficiency and stresses on the switches are reduced. It consists of multi-
input circuit, low voltage (LV) bridge and high voltage (HV) bridge. The LV and
HV bridges are connected together by high-frequency transformer with 1: n ratio.
If equal rating of number of battery is connected at the input, the maximum and
minimum power in combinational mode is given by Eqs. (19) and (20).
Pmin = 2 ∗ Pn (19)
Pmax = m ∗ Pn (20)
where Pn is the standard power of a single battery. The dual-phase shift modulation
is used to control power flow using inner phase shift ratio d1 and outer phase shift
ratio d2.
Table 1 gives the comparison between the topologies mentioned in the references.
9. 728 S. Sathishkumar et al.
Table
1
Summary
of
discussed
topologies
Topology
Advantages
Disadvantages
Efficiency
Duty
cycle
No.
of
components
Ref.
[1]
•
High
efficiency
in
wider
region
•
Only
few
operating
modes
exhibit
soft-switching
characteristics
Highly
efficient
Normalized
switching
frequency
is
around
0.7
S-12,
L-2,
C-4
Ref.
[2]
•
Minimum
switching
losses
due
to
soft
switching
•
High
efficiency
over
a
wide
range
of
voltage
gain
•
In
reverse
mode,
ZVS
(soft
switching)
is
not
achieved
small
range
•
Decision
algorithm
is
needed
to
select
the
mode
of
operation
98.3
and
98.2%
efficiency
for
forward
and
reverse
power
flow
Switching
frequency
is
100
kHz
S-8,
L-2,
C-5
Ref.
[3]
•
ZVS
achieved
for
all
switches
•
Reduced
circulation
loss
•
Magnetic
bias
issue
96.71%
in
charging
mode
and
96.79%
in
discharging
mode
The
maximum
transferred
power
can
be
obtained
when
D
=
0.5
S-8,
L-4,
C-4,
D-2
Ref.
[4]
•
Achieved
zero
voltage
transition
•
Limited
soft-switching
operation
range
95.5%
at
full
load
Switching
frequency
=
200
kHz
S-6,
L-5,
C-4
Ref.
[5]
•
Least
number
of
switches
•
Soft
switching
for
main
switch
•
Proper
controllers
are
needed
Achieved
peak
efficiency
of
94.5%
Switching
frequency
varies
from
100
to
170
kHz
S-3,
L-4,
C-5,
D-4
Ref.
[6]
•
Soft
switching
•
Capacitor
is
needed
for
soft
switching
Switching
frequency-195–310
kHz
S-9,
L-3,
C-9
Ref.
[7]
•
Low
voltage
stress
on
switches
•
High
step-up
and
step-down
ratio
•
Assumptions
are
made
which
are
not
suited
in
practical
95.5%
for
boost
operation
and
95%
for
buck
operation
Switching
frequencies
are
105
kHz
(boost)
and
140
kHz
(buck)
S-4,
L-3,
C-6
(continued)
10. An Overview of Different Topologies of DC/DC Bidirectional … 729
Table
1
(continued)
Topology
Advantages
Disadvantages
Efficiency
Duty
cycle
No.
of
components
Ref.
[8]
•
Soft
switching
•
Switching
frequency
should
be
kept
higher
than
the
normal
values
The
peak
efficiency
was
97.7%
under
battery
charging
mode
(BCM)
and
98.1%
under
regeneration
mode
(RM)
The
operating
frequency
range
for
BCM
is
85–145
kHz
and,
RM
is
40–110
kHz
S-8,
L-3,
C-4
Ref.
[9]
•
Reduction
in
circulation
power
and
peak
current
stress
•
Multi-input
configuration
•
High
cost
93.5%
efficiency
at
independent
mode
Switching
frequency
is
20
kHz
S-14,
L-1,
C-2
S—Switch;
L—Inductor;
C—Capacitor;
D—Diode
11. 730 S. Sathishkumar et al.
3 Conclusion
In this paper, several numbers of topologies of bidirectional DC/DC converter are
presented. The advantages and their working are discussed. The bidirectional con-
verter satisfies the demand for energy storage and sends back to the grid or battery
discharging. Zero voltage transition reduces the power dissipation during switching.
It is used to interface the different sources to the grid system for sending and receiving
power from and to the grid.
References
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converter suitable for wide voltage gain range. IEEE Trans. Power Electron. 33(4) (2018)
3. Sha, D., Chen, D., Zhang, J.: A bidirectional three-level DC–DC converter with reduced cir-
culating loss and fully ZVS achievement for battery charging/discharging. IEEE J. Emerg. Sel.
Top. Power Electron. 6(2) (2018)
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